Green Tea Epigallocatechin Gallate Inhibits Insulin Stimulation of Adipocyte Glucose Uptake via the 67-Kilodalton Laminin Receptor and AMP-Activated Protein Kinase Pathways

Abstract

Insulin and (−)-epigallocatechin gallate (EGCG) are reported to regulate obesity and fat accumulation, respectively. This study investigated the pathways involved in EGCG modulation of insulin-stimulated glucose uptake in 3T3-L1 and C3H10T1/2 adipocytes. EGCG inhibited insulin stimulation of adipocyte glucose uptake in a dose- and time-dependent manner. The concentration of EGCG that decreased insulin-stimulated glucose uptake by 50–60 % was approximately 5–10 µM for a period of 2 h. At 10 µM, EGCG and gallic acid were more effective than (−)-epicatechin, (−)-epigallocatechin, and (−)-epicatechin 3-gallate. We identified the EGCG receptor [also known as the 67-kDa laminin receptor (67LR)] in fat cells and extended the findings for this study to clarify whether EGCG-induced changes in insulin-stimulated glucose uptake in adipocytes could be mediated through the 67LR. Pretreatment of adipocytes with a 67LR antibody, but not normal rabbit immunoglobulin, prevented the effects of EGCG on insulin-increased glucose uptake. This suggests that the 67LR mediates the effect of EGCG on insulin-stimulated glucose uptake in adipocytes. Moreover, pretreatment with an AMP-activated protein kinase (AMPK) inhibitor, such as compound C, but not with a glutathione (GSH) activator, such as N-acetyl-L-cysteine (NAC), blocked the antiinsulin effect of EGCG on adipocyte glucose uptake. These data suggest that EGCG exerts its anti-insulin action on adipocyte glucose uptake via the AMPK, but not the GSH, pathway. The results of this study possibly support that EGCG mediates fat content.

Key words

green tea - Camellia sinensis - Theaceae - epigallocatechin 3‐gallate - insulin - glucose uptake

References

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1 These authors contributed equally to this work.